1. Field of the Invention
The present invention relates to a loudspeaker system for audio appliances, television receivers, etc., and more particularly, to a loudspeaker system which can improve the bass sound characteristics and increase the straight-traveling property of radiated sound waves by amplifying the sound waves discharged from the rear of a loudspeaker.
2. Description of the Related Art
Generally, a loudspeaker converts an electric signal into a sound wave signal and radiates the sound wave signal into free space. A cone type loudspeaker is the most frequently used conventional loudspeaker. In a cone type loudspeaker, if a strong cylindrical magnetic field is created in a magnet which is located between a center pole and a yoke, as current is applied to a voice coil which is disposed in the magnetic field, force is induced to vibrate a conical vibrating board, made of paper, for example, to thereby radiate sound waves.
Since the force is constant regardless of a frequency, it is possible to obtain flat frequency characteristics over a wide range of frequencies. The low frequency zone of the loudspeaker system is restricted by a minimum resonance frequency determined by an equivalent mass including a radiation mass and a compliance due to edge, damper, etc. The high frequency zone is restricted by divided vibration due to a limit in the rigidity of a cone paper.
In divided vibration, since a small diameter of the cone paper yields a higher frequency, loudspeakers having the same structures and different cone diameters are used in combination to radiate sound waves having a wider range of frequencies.
In addition to the minimum resonance frequency, the low frequency zone radiation is influenced by the size of a cabinet containing the loudspeaker. This is because when the cone is vibrated to radiate the sound waves, counter phases are generated in the forward and rearward directions from the cone, and may interfere with each other, so that the sound waves are not properly radiated in the low frequency zone.
Accordingly, to obtain the sound waves of a low frequency, the size of the cabinet must be somewhat large. This prevents an audio appliance, television receiver, etc., from being compact.
A conventional loudspeaker system for amplifying sound waves radiated from the rear of a loudspeaker, as shown in FIG. 1, includes a loudspeaker 2, disposed inside a loudspeaker cabinet 1, for radiating the sound waves, a wave guide 3 for transmitting the sound waves radiated from the rear of the loudspeaker 2, and a horn 4 for amplifying the transmitted sound waves.
The sound waves generated from the loudspeaker 2 are radiated from the front of the loudspeaker 2 and simultaneously from the rear of the loudspeaker 2. The sound waves radiated from the rear of the loudspeaker 2 are transmitted for a predetermined distance through the wave guide 3, and then are radiated to the front portion of the cabinet 1 through the horn 4.
However, the conventional loudspeaker system as constructed above suffers from drawbacks in that although a portion of the bass sound waves radiated from the rear of the loudspeaker can be amplified to some extent, since the sound waves radiated from the rear of the loudspeaker are totally transmitted through the wave guide 3 and the horn 4, serious interference occurs between the sound waves radiated from the rear of the loudspeaker that have a frequency lower than a desired level. Particularly, bass of a very low level can not be properly amplified and the clarity of the resulting sound deteriorates severely due to the distortion of the sound waves.
Also, the straight-traveling property of the sound waves radiated through the loudspeaker 2 and the horn 4 deteriorates due to interference generated therebetween, and thus the sound waves cannot be transferred over a long distance.